Sheet supplying device and image forming apparatus

ABSTRACT

A sheet supplying device which supplies a sheet, including: a sheet supplying tray which stacks a bundle of sheets; a first air blowing section which blows air against a side of the bundle of sheets stacked on the sheet supplying tray; a second air blowing section which blows air from downstream of the bundle of sheets in a sheet conveyance direction, onto a leading section of the sheets; a vacuum conveyance section which vacuums an uppermost sheet of the bundle of sheets and conveys the sheets one by one; a shielding member which shields air blown from the first air blowing section; a vacuum detection sensor which detects that a sheet has been vacuumed by the vacuum conveyance section; and a control section which controls the shielding member to open so that air generated by the first air blowing section is blown to the bundle of sheets.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2007-083,975 filed on Mar. 28, 2007, with the Japanese Patent Office, the entire content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a sheet supplying device which is used for image forming apparatuses, such as copy machines, printers, facsimiles, printing machines, and multifunctional peripherals, and in particular, to a sheet supplying device which is able to separate to separate recording sheets, such as coated paper, and convey them one by one.

BACKGROUND OF THE INVENTION

The sheet supplying device, which is able to feed sheets one by one by a sheet supplying roller from a bundle of sheets including plural stacked sheets, is provided on the above image forming apparatuses. If plural sheets are fed from said sheet supplying device, sheet jamming tends to result. Further, if the feeding force is inadequate, miss-feeding results. Accordingly, a device must be designed which can unfailingly feed sequential sheets. To overcome this problem, the friction factor between the sheet and the sheet supplying roller is increased so that the uppermost sheet of the bundle of sheets can be fed one by one so that miss-feeding is prevented. In order not to feed two or more sheets at the same time, a separating roller, patting separation or a sheet separating claw is provided so that the lower stacked sheets are pushed back, and only the uppermost sheet is fed out.

This method is effective for normal plain sheets. However, not only coated sheets but also various types of sheets are typically used, because of expanded application of the copiers or printers in recent years. Such sheets have great mutual attractive force when they are bundled, whereby the above-described sheet supplying devices occasionally cannot prevent occurrence of feeding such mutually attracted sheets.

To overcome this problem, a method is disclosed in which an air blower is provided on a side of a sheet conveyance section, whereby air is blown onto plural sheets existing on the upper section of the bundle of sheets, whereby air passes between the mutually attracted sheets so that they are separated from each other.

Consequently, only separate sheets are conveyed to the image forming section by the sheet supplying roller. Further, on a large printing machine, a suction section is provided, which sucks up the uppermost sheet for conveyance.

However, coated sheets has characteristics in which overlapped sheets are strongly adhered to each other in high humidity environment. Such relatively strongly adhered sheets are not separated from each other by a weak force of air, so that the uppermost sheet is not separated from the lower sheet.

To overcome this problem, strong air should needs to be applied between the clearance of the adhered sheets. However, said strong force of air excessively pushes the sheet sucked onto a suction belt from below.

In the cases when air is blown to the clearance between sheets which are weakly adhered to each other, so that the sheets are separated as a bundle of sheets, if air is blown from the front to separate the adhered sheets, separating air to rub down the sheet and upholding air to hold up the bundle of sheets interfere with each other, so that sheet separation is not effectively conducted, and two or more adhered sheets are fed, which can be a major problem.

Unexamined Japanese Patent Application Publication No. 2004-131,291 discloses a sheet vacuum conveyance device which incorporates a sheet vacuum conveyance section which draws up sheets one by one from a bundle of sheets stacked in sheet stacking section, and a variable air flow section which can change air flow velocity, whereby when the air flow velocity is less than a predetermined value, sheet conveyance is conducted so that only the uppermost sheet is separated by the sheet vacuum conveyance section.

In order to exhibit a reliable sheet separating function, an appropriate amount of blown air should be selected based on sheet size, sheet basis weight, and sheet surface roughness. However, if the sheet status changes due to environmental temperature and humidity, said selected appropriate amount also changes. Further, due to sheet curl, sheet perforations or striated lines existing on the sheet, and powder scattered on off-set printed sheets, the appropriate amount of air flow differs. Accordingly, since the appropriate required air flow amount tends to vary, it is almost impossible to automatically set an appropriate amount for each sheet, though the sheet supplying device memorizes the appropriate amount of air for each sheet.

Specifically, in a case of re-print in off-set printing, the powder adheres on the sheet supplying roller so that the sheet conveyance force tends to decrease. Further, the sheets move upward in a stacked state, so that the sheets are not effectively separated. Yet further, the appropriate conditions do not go together for some types of sheets.

In a method in which the air direction or air flow velocity is changed to separate the sheets, the air direction or air flow velocity tends to be resistant for the sheet conveyance.

Further, since these air blowing means are mounted on a sheet supplying tray which can be withdrawn from the sheet supplying device, the sheet supplying device becomes larger, therefore the image forming apparatus incorporating said sheet supplying device easily becomes larger. Yet further, said air blowing means can be easily mounted on large-sized machines, while they can rarely be mounted on small-sized machines.

In the sheet supplying device of the above-described patent document, the air blowing means blows air toward the side of the leading sections of the sheets stacked on the sheet supplying tray. However, for coated sheets, thicker sheets with higher basis weight, large-sized sheets, and film for OHP, the air blow directed toward the side of the leading sections of the sheets is often not enough to separate the adhered sheets, so that sheet conveyance tends to be unacceptable.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the above problems, by providing a sheet supplying device which can separate the stacked sheets, in accordance with sheet size, basis weight and surface roughness, and can stably feed sheets one by one.

The object of the present invention will be attained by the structures described below.

Structure 1. A sheet supplying device which supplies the recording sheets includes:

a recording sheet supplying tray which stacks a bundle of sheets including plural recording sheets,

a first air blowing section which blows air against a side of the bundle of sheets stacked on the recording sheet supplying tray,

a second air blowing section which blows air, from a position downstream of the bundle of sheets in a sheet conveyance direction, onto leading sections of the recording sheets,

a vacuum conveyance section which vacuums the uppermost sheet of the bundle of sheets stacked on the sheet supplying tray and conveys the recording sheets one by one in the sheet conveyance direction,

a shielding member which shields against air blown by the first air blowing section,

a vacuum detection sensor which detects that a recording sheet has been vacuumed by the vacuum conveyance section, and

a control section which controls the shielding member to open or close so that air generated by the first air blowing section is blown onto the bundle of sheets.

Structure 2. An image forming apparatus includes:

an image forming section which forms an image on an image carrier,

a transfer section which transfers a toner image on the image carrier onto a recording sheet,

a sheet supplying device which conveys the image carrying sheet to the transfer section, and

a fixing device which heats and fixes the toner image carried by the recording sheet,

wherein the sheet supplying device includes:

a recording sheet supplying tray which stacks a bundle of sheets including plural recording sheets,

a first air blowing section which blows air against a side of the bundle of sheets stacked on the recording sheet supplying tray,

a second air blowing section which blows air, from a position downstream of the bundle of sheets in the recording sheet conveyance direction, onto the leading sections of the bundle of sheets with respect to the recording sheet conveyance direction,

a vacuum conveyance section which vacuums the uppermost sheet of the bundle of sheets stacked on the recording sheet supplying tray and conveys the recording sheets one by one,

a shielding member which shields against air blown by the first air blowing section,

a vacuum detection sensor which detects that a recording sheet has been vacuumed by the vacuum conveyance section, and

a control section which controls the shielding member to open or close so that air generated by the first air blowing section is blown against the bundle of sheets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a total view of an image forming apparatus, structured of an image forming apparatus as a main body, an image reading device, an automatic document feeding device, and a large-capacity sheet supplying device.

FIG. 2 is a perspective view showing a main section of the sheet supplying device of the present invention.

FIG. 3 is a cross sectional front view of the sheet supplying device.

FIG. 4 is a plain view of the sheet supplying device.

FIG. 5 is a side view of the sheet supplying device.

FIGS. 6( a) and 6(b) are cross sectional drawings which show the vacuum conveyance of a sheet conducted by the first air blow section and the second air blow section.

FIG. 7 is a block diagram showing the control of the sheet supplying device.

FIG. 8 is a timing chart showing the control of the sheet supplying device.

DETAILED DESCRIPTION OF THE INVENTION

The embodiment of the present invention will now be detailed while referring to the drawings, however, the present invention is not limited to the embodiments detailed below.

The embodiment of the present invention will now be detailed while referring to the drawings.

[Image Forming Apparatus]

FIG. 1 shows a total view of an image forming apparatus, structured of image forming apparatus A as a main body, image reading device SC, automatic document feeding device DF, and large capacity sheet supplying device LT.

Image forming apparatus A as a main body is structured of an image forming section, including photoconductor 1 serving as an image carrier, charging section 2, exposure device 3, developing device 4, image transfer section 5, and cleaning section 6, fixing device 7 and a sheet conveyance section.

Said sheet conveyance section is structured of sheet supplying cassette 10, first sheet supplying section 11, second sheet supplying section 12, sheet ejection section 14, conveyance route switching section 15, sheet circulating re-supplying section 16, and sheet reverse-ejection section 17.

Document d, placed on the glass platen of automatic document feeding device DF, is conveyed to exposure device 3 by the sheet supplying section, where the image on a single surface or both surfaces is exposed by an optical system of image reading device SC, and is read by image sensor CCD. Analog signals, photo-electrically converted by image sensor CCD, are processed by image processing section 20, with respect to the analog process, A/D conversion, shading correction process, and image compressing process, then said signals are sent to the image forming section as image signals.

In the image forming section, various processes are conducted, such as electrical charge, exposure, developing, image transferring, sheet separation, and cleaning.

In the image forming section, the surface of photoconductor 1 is electrically charged by charging section 2, on which an electrostatic latent image is formed by laser beams emitted from exposure device 3, subsequently, said latent image is developed by developing device 4 as a toner image. A recording sheet P, stored in sheet supplying cassette 10, is conveyed by first sheet supplying section 11. Further, recording sheet P is conveyed while being synchronized with the toner images, by second sheet supplying section 12, represented by paired registration rollers. After the toner image is transferred onto recording sheet P by image transfer section 5, said toner image is fixed onto recording sheet P by fixing device 7 to be a permanent image.

Then recording sheet P carrying the fixed image is ejected outside the apparatus by sheet ejection section 14. Any residual toner remaining on photoconductor 1 is removed by cleaning section 6. In a case of double-sided prints, recording sheet P, carrying a toner image on a first surface, is conveyed to circulation re-supplying section 16 to be reversed, and another image is formed on a second surface by the image forming section, after which recording sheet P carrying a image on both surfaces is ejected outside the apparatus by sheet ejection section 14. In the case of reversed sheet ejection, recording sheet P, carrying one fixed image, is directed to another route, and is switched-back by reversed sheet ejection section 17 so that sheet P is reversed, then sheet P is also ejected outside the apparatus by sheet ejection section 14.

Large capacity sheet supplying device LT, which is the sheet supplying device of the present invention, is connected to image forming apparatus A serving as a main body. Large capacity sheet supplying device LT, incorporating sheet supplying device 30 serving as a main body, first air blow section 40, second air blow section 50, and vacuum conveyance section 60, stores a large capacity of recording sheets P, and supplies said recording sheets P one by one to image forming apparatus A.

Sheet supplying device 30 serving as a main body incorporates sheet supplying tray 31, leading sheet edge regulation member 33, trailing sheet edge regulation member 33, and guide rails 34. Sheet supplying tray 31 is formed of three stages, wherein each sheet supplying tray 31 can be pulled out from sheet supplying device LT by guide rails 34. The maximum capacity of sheet supplying device LT is approximately 10,300 sheets.

FIG. 2 is a perspective view showing a main section of sheet supplying device LT of the present invention, FIG. 3 is a cross sectional front view of sheet supplying device LT, FIG. 4 is a plain view of sheet supplying device LT, and FIG. 5 is a side view of sheet supplying device LT.

In the above figures, recording sheets P are stacked on sheet supplying trays 31, and said trays 31 can be elevated by an un-illustrated elevating mechanism. Side section regulation members 41 can be driven perpendicular to the sheet conveyance direction, that is, in the present invention, they can be driven in the width direction of sheet P. Accordingly, side section regulation members 41 regulate the recording sheets P by softly pushing both sides of sheet P. Leading sheet edge regulation member 32 regulates the position of the leading edge of sheet P in the sheet conveyance direction. Trailing sheet edge regulation member 33 can be driven in the sheet conveyance direction so that it regulates the position of the trailing edge of sheet P in the sheet conveyance direction.

Further, as shown in FIG. 3, height detecting sensor PS3 is mounted on said trailing sheet edge regulation member 33, which detects the height of uppermost sheet P.

In order to make the height of stacked sheets P on sheet supplying tray 31 to be suitable for air blow and for blowing sheets P, a control section to be discussed later controls an un-illustrated motor to vertically drive sheet supplying tray 31, based on the result detected by height detection sensor PS3, shown in FIG. 7.

As shown in FIG. 3, vacuum conveyance section 60 is mounted near an outlet of sheets P. Vacuum conveyance section 60 incorporates large drive roller 61 driven by a motor, two small rollers 62, and vacuuming belt 63 which is entrained about rollers 61 and 62. A large number of small holes penetrate vacuuming belt 63. Vacuuming device 64 is mounted inside vacuuming belt 63, so that sheet P is drawn and conveyed by vacuuming belt 63.

When vacuuming belt 63 is rotated while sucking sheet P, uppermost sheet P of the sheets stacked on sheet supplying tray 31 is driven in arrowed direction X so that said sheet P is ejected to image forming apparatus A.

Vacuum detection sensor PS1, mounted near the vacuuming surface of vacuuming belt 63, detects that uppermost sheet P has been vacuumed.

Sheet feed sensor PS2, mounted near vacuuming belt 63 downstream of the sheet conveyance direction of sheet supplying tray 31, detects the passage of recording sheet P.

Within sheet supplying device 30, second air blow section 50 is mounted, near vacuuming belt 63 downstream of the sheet conveyance direction of sheet supplying tray 31. Second air blow section 50 is structured of a fan and motor unit and the like. In addition, it is possible to structure the embodiment in which second air blow section 50 is mounted on sheet supplying device 30, and air blow is sent through a duct toward the leading edge of stacked sheets P.

Fan and motor unit 51 of second air blow section 50 is mounted so that its air outlet 53 faces upward. Air blown upward is turned in direction by guide plate 52, whereby air is blown obliquely upward from air outlet 53, that is, air is blown into the area adjacent to vacuuming belt 63 of vacuum conveyance section 60.

Second air blow section 50 is controlled based on the type of recording sheet P. When OHP films, tracing sheets, smooth coated sheets, perforated sheets, striated sheets, and powdered sheets after off-set print are used, second air blow section 50 blows air between sheets P so that uppermost sheet P is separated from the adjacent lower sheet.

As shown in FIGS. 2 and 5, first air blow sections 40 are arranged on both sides of sheet supplying tray 31, so that first air blow sections 40 blow air perpendicular to the sheet conveyance direction, at the top area of sheet P stacked on sheet supplying tray 31. First air blow section 40 incorporates fan and motor unit 42 which blows air against the top area of sheet P through air blow outlets 44, both of which are located perpendicular to the conveyance direction of sheet P.

First air blow section 40 is mounted on side section regulation member 41. Fan and motor unit 42 is mounted so that air blow outlet 44 faces upward. Air blow directed upward is turned 900 by guide plate 43, and is horizontally blown from air outlet 44. Air outlets 44 are positioned near the top end of side section regulation members 41. The width of air blow outlet 44 is the same as the width of the outlet of first air blow section 40. It is preferable for sheet separation that uppermost sheet P is nearly at the vertical center of air blow outlet 44. Since first air blow section 40 is mounted on side section regulation member 41, even when the size of sheet P is varied, first air blow section 40 can be shifted with side section regulation member 41. In this embodiment, first air blow section 40 and air blow outlet 44 are mounted on both sides of sheets P, but may also be mounted on only a single side of sheets P.

When first air blow section 40 is activated, air is blown out from air outlet 44 so that several stacked sheets P of the uppermost section are blown by air. Air passes through several of the top stacked sheets P from one side to the other side. Due to this air passage, several sheets P on the uppermost section are separated. Vacuum conveyance section 60 lifts up the single uppermost sheet P which has been separated from the sheet below it by the above function, and unfailingly conveys said uppermost sheet P toward downstream sections.

As shown in FIGS. 2 and 3, an air inlet of first air blow section 40, covered with a shielding member, is openable and closable. That is, shutter 45, serving as said shielding member, pivots on shaft 46, and is opened or closed by solenoid SOL. The control sect ion controls shutter 45 to be open or closed so that first air blow section 40 can blow air or not.

FIGS. 6( a) and 6(b) are cross sectional drawings which show the vacuum conveyance of sheet P conducted by first air blow section 40 and second air blow section 50.

FIG. 6( a) shows a vacuuming operation of sheet P. Several of uppermost sheets of stacked sheets P are blown up by first blowing air V1 blown by first air blow section 40 (first blowing air V1 is illustrated by a large outlined arrow), and said several sheets P are drawn up by vacuuming air V3 coming through vacuuming belt 63 (vacuuming air V3 is illustrated by a smaller outlined arrow). Second air blow V2 coming from second air blow section 50 is applied to the bottom section of vacuuming belt 63 (second air blow V2 is illustrated by a longer outlined arrow).

FIG. 6( b) shows the separating operation of sheets P. When shutter 45 closes the air inlet of first air blow section 40 to stop air flow, only air from second air blow section 50 passes between uppermost sheet P1 and sheets P2 below sheet P1, which have been lifted up. Uppermost sheet P1 is still vacuumed by vacuuming air V3, separated from other sheets P2. Sheets P2, including the below sheets, drop due to their own weight onto remaining sheets P which were not vacuumed.

The above-described air blow operations, conducted by first air blow section 40 and second air blow section 50, are repeated so that blown air allows several sheets P2 of the uppermost section of the stacked sheets to float near the total sections of air outlets 44 and 53, whereby the clearances between each sheet P become equal. Air passes through said clearances. Due to this, the top sheet P1 can be separated from the stack of sheets, and is easily conveyed. Accordingly, scarring on the sheet due to extraordinary flowing is prevented, and the plural adhered sheets are prevented from being lifted up, so that they are safely separated from each other.

After sheet P1 is separated from sheet P2 directly below it, vacuum conveyance section 60 is activated by an un-illustrated driving section, so that single sheet P1 vacuumed by vacuuming belt 63 is conveyed.

FIG. 7 is a block diagram showing the control of the sheet supplying device, while FIG. 8 is a timing chart showing the control of the sheet supplying device.

When vacuum detection sensor PS1 detects that vacuuming belt 63 of vacuum conveyance section 60 has vacuumed sheet P1, the control section controls shutter 45 to open or close, whereby air is switched to blow or not to blow from first air blow section 40.

From the moment when vacuum detection sensor PS1, mounted near vacuuming belt 63, detects that vacuum conveyance section 60 has vacuumed sheet P1, to the moment when vacuum conveyance section 60 starts conveyance of sheet P1, the control section controls shutter 45 to close the air inlet of first air blow section 40 so that air blow is not conducted.

Further, when feed sensor PS2 has not yet detected sheet P1, though vacuum detection sensor PS1 detected that sheet P1 has been vacuumed, that is, only before sheet P1 is conveyed, the control section activates shutter 45 to open so that the air blow is conducted.

In addition, the time that shutter 45 is closed does not need to be the same as the above described timing, but if it is limited to a moment when the conveyance of sheet P1 starts, the closed duration is so short that sheet P1 is not effectively separated. Further, if shutter 45 is always closed when vacuum detection sensor PS1 detects that sheet P1 has been vacuumed, the air blow is not sufficient to lift sheet P1 up so that vacuuming belt 63 cannot lift sheet P1, which results in irregular supply of sheets. That is, both long closed duration of shutter 45 and short closed duration of shutter 45 result in unreliable supplying of sheets. For the best closed duration, as shown in FIG. 7, concerning first sheet P1, while vacuum detection sensor PS1 detects sheet P1 (which means sensor PS1 is ON), and feed sensor PS2 has not yet detected sheet P1 (which means sensor PS2 is OFF), which is before the conveyance, the control section activates solenoid SOL to close shutter 45. When feed sensor PS2 detects sheet P1 (which means sensor PS2 is ON), the control section activates solenoid SOL to open shutter 45.

Next, a second sheet P2 is ejected, that is, vacuum detection sensor PS1 switches from ON to OFF, and a predetermined duration has passed after feed sensor PS2 turns OFF, vacuum detection sensor PS1 then detects a third sheet P3 (which means sensor PS1 is again ON), and the control section activates solenoid SOL to close shutter 45.

For the sheet supplying device of the present invention, namely large capacity sheet supplying device LT, combined with image forming apparatus A, is used for the above explanations, however, this invention can also be used for sheet cassette 10 incorporated within image forming apparatus A.

As describe above, the effect of the invention is shown below.

The shielding member mounted on the air flow section is controlled to open or close, while the air flow speed is increased. Though a strong upholding air force is directed against the bundle of sheets, when the separating air flow is applied to separate a sheet, the upholding air flow is shielded. Accordingly, the upholding air flow does not interfere with the separating air flow, so that the sheets are effectively separated and fed.

By this structure, even in a high humidity environment causing the attracted recording sheets, even coated sheets can be unfailingly fed one by one.

Further, in the image forming apparatus having said sheet supplying device, the recording sheets are fed one by one, independently to the type of sheet, enabling the image forming section to assuredly form an image on the recording sheet. 

1. A sheet supplying device which supplies a sheet, comprising: a sheet supplying tray which stacks a bundle of sheets; a first air blowing section which blows air against a side of the bundle of sheets stacked on the sheet supplying tray; a second air blowing section which blows air from a position downstream of the bundle of sheets in a sheet conveyance direction, onto a leading section of the sheets; a vacuum conveyance section which vacuums an uppermost sheet of the bundle of sheets stacked on the sheet supplying tray and conveys the sheets one by one in the sheet conveyance direction; a shielding member which shields against air blown by the first air blowing section; a vacuum detection sensor which detects that a sheet has been vacuumed by the vacuum conveyance section; and a control section which controls the shielding member to open or close so that air generated by the first air blowing section is blown to the bundle of sheets or not.
 2. The sheet supplying device of claim 1, wherein when the vacuum detection sensor detects that the sheet has been vacuumed by the vacuum conveyance section, the control section controls the shielding member so that air is not blown from the first air blow section.
 3. The sheet supplying device of claim 1, wherein the first air blow section comprises an air inlet and an air outlet, and the shielding member comprises a shutter which shields the air inlet or the air outlet.
 4. An image forming apparatus, comprising: an image forming section which forms an image on an image carrier; a transfer section which transfers a toner image on the image carrier onto a sheet; a sheet supplying device which conveys the sheet to the transfer section; and a fixing device which heats and fixes the sheet carrying the toner image, wherein the sheet supplying device comprises: a sheet supplying tray which stacks a bundle of sheets including plural sheets; a first air blowing section which blows air against a side of the bundle of sheets stacked on the sheet supplying tray; a second air blowing section which blows air, from a position downstream of the bundle of sheets in a sheet conveyance direction, onto leading sections of the sheet; a vacuum conveyance section which vacuums an uppermost sheet of the bundle of sheets stacked on the sheet supplying tray and conveys the sheets one by one in the sheet conveyance direction; a shielding member which shields air blown by the first air blowing section; a vacuum detection sensor which detects that a sheet has been vacuumed by the vacuum conveyance section; and a control section which controls the shielding member to open or close so that air generated by the first air blowing section is blown to the bundle of sheets or not.
 5. The image forming apparatus of claim 4, wherein when the vacuum detection sensor detects that the sheet has been vacuumed by the vacuum conveyance section, the control section controls the shielding member so that air is not blown from the first air blow section.
 6. The sheet supplying device of claim 1, wherein the first air blow section comprises an air inlet and an air outlet, and the shielding member comprises a shutter which shields the air inlet of the air outlet. 